Process for producing foam cigarette filters



y 1, 1966 A. R. BLAKEY, JR ET AL 3,253,967

PROCESS FOR PRODUCING FOAM CIGARETTE FILTERS Filed Dec. 18, 1962 INVENTORS ERNEST ALBERT COLEMAN JI ANGUS RUCKER BLAKEY, JR.

BY M414. 7%,

ATTORNEY United States Patent 0.

3,253,967 PROCESS FOR PRODUCING FOAM CIGARETTE FILTERS Angus Rucker Blakey, Jr., Kennett Square, Pa., and Ernest Albert Coleman 11, Fairfax, DeL, assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Dec. 18, 1962, Ser. No. 245,481 5 Claims. (Cl. 1561) This invention relates to polyoxymethylene foams and their use in forming filters.

In the past, foams of synthetic resins have had closed cell structures at moderate densities. When such foams are crushed or otherwise treated to form an open cell structure, a foam having an irregular distribution of sizes of passages between cells results or the material crushes as in the case of closed cell polystyrene foams. Hence, controlling the performance of these foams in certain uses has been difficult.

It is an object of this invention to provide a ruptured cell, resilient, low density, thermoplastic, high modulus foam having a uniform distribution of cells of controllable size. A further object of this invention is to provide a ruptured cell foam cigarette filter. Another object is to provide a filter medium suitable for various gas and liquid filtration applications.

These and other objects are accomplished by the following invention in which a polyoxymethylene resin is extruded as a foam by injecting a fluid blowing agent into the resin melt just prior to extrusion (normally in the die end of the extruder). The resin preferably is blended with a nucleating agent prior to extrusion.

The polyoxymethylene resins used in this invention are polymers and copolymers having a structure in which all of the recurring units have the formula:

2,734,889, issued February 14, 1956, to F. C. Starr, Jr. 2,768,994, issued October 30, 1956 to R. N. MacDonald 2,828,286, issued March 25, 1959 to R. N. MacDonald 2,841,570, issued July 1, 1958 to R. N. MacDonald 2,844,561, issued July 22, 1958 to M. F. Bechtold et al. 2,848,437, issued August 19, 1958 to W. P. Langsdorf et al. 2,994,687, issued August 1, 1961 to H. H. Goodman et al. 3,000,860, issued September 19, 1961 to N. Brown et al. 3,000,861, issued September 19, 1961 to N. Brown et al.

One variety of polyoxyrnethylene, i.e., polyoxymethylene diesters may be prepared by the processes described and claimed in United States Patents 2,964,500, issued December 13, 1960, to S. H. Jenkins et al., and 2,998,409, issued August 29, 1961, to S. Dal Nogare et al. Polyoxymethylene diethers may be prepared by the processes described and claimed in copending patent applications Serial No. 682,325, filed September 6, 1957, by N. Brown et al., and Serial No. 785,136, filed January 6, 1959, by N. Brown et al. Included within the term polyoxymethylene for purposes of this application are copolymers containing a predominance of oxymethylene groups, such as those prepared by the techniques set forth in United States Patents 2,828,287, issued March 25, 1958, to T. L. Cairns et al., 3,027,352, issued March 27, 1962, to K. W. Bartz et al., and 3,043,803, issued July 10, 1962, to C. D. Lewis et al., and in copending applications. Y

Ser. No. 35,419, filed June 13, 1960, by N. Brown et al. Ser. No. 35,420, filed June 13, 1960, by N. Brown et al. Ser. No. 35,421, filed June 13, 1960, by E. T. Cline et al. Ser. No. 51,294, filed August 23, 1960, by E. T. Cline et al. Ser. No. 91,318, filed February 24, 1961, by E. T. Cline.

exhibit a pH greater than 4 when slurried in distilled water (pH 7) at 1% concentration, metal powders, flakes and shot. Suitable metals include copper, iron, nickel and lead. The fillers may be in the form of powders, flakes, fibers, sheets or foams such as micro-balloons made of phenolic resins.

Colorants may be used including those which give a sludge pH of 4 or greater at 1% concentration. Useful classes of such colorants include pigments, dyes, pigmentdyes, metal-flakes, fluorescent materials, and carbon.

Processing aids may be used including'additives which (a) decrease processing temperatures of the acetal resin, (b) increase or aid in the solubility of the blowing agents in the resin, (0) increase the melt strength or melt elasticity of the resin, or (d) decrease or increase friction or stick-slip of the resin melt against the material of construction of the extruder die orifice. Processing aids include aromatic hydrocarbons melting below 200 C. and boiling above 135 C. such as naphthalene and polymeric materials including polystyrene; materials of the same groups as blowing agents, hereinafter described, but melting below 200 C. and boiling above about 135 C. such as benzyl alcohol, glycerine, sulfur, and neutral or basic surface-active agents, such as silicone oil and polyalkene oxide adducts of alkylated phenols.

Suitable nucleating agents preferably are solids of high surface area, preferably 0.28 square meters per gram or greater and which produce more cells in the foam than would be produced in their absence. Examples of these materials include carbon black having a surface area of 0.1 to 30 m. /g., Fiberglas having a surface area of 0.5 to m. /g., and talc, H Mg (SiO having a surface area of 0.01 to 20 m. g.

Suitable blowing agents are fluids which dissolve in acetal resin at temperatures of 150 to 250 C. at pressures of 1 to atmospheres and have boiling points at atmospheric pressure of less than C. Such blowing agents are selected from the classes consisting of water, ketones, alcohols, aldehydes, esters, halogenated hydrocarbons, nitriles, gases, such as carbon dioxide, nitrogen, ammonia, and formaldehyde and combinations thereof. Included in these classes are aqueous solutions of formaldehyde, aqueous solutions of ammonia (ammonium hydroxide) and aqueous solutions of methyl ethyl ketone. Also included in these classes are dichlorodifiuoromethane, dichloromethane, chloroform, fluorotrichloromethane, 1,1,1-trichloroethane, 1,1,2-trifluoroperchloroethane, ethanol, butanol-Z, ethyl acetate, acet- 3 aldehyde, ethyl chloride and acetonitrile. Of these, water, methyl ethyl ketone, methylene chloride, chloroform, methyl ethyl ketone in water, and chloroform in dichlo-romethane are preferred with water being especially pre- 4 filter 13 in FIGURE 4. In the preferred method a plurality ('3-6) of ribbons are wrapped with paper and cut to length to form a filter similar to that illustrated in FIGURE 4.

ferred. Water is especially preferred because it has a The following examples are illustrative of the invenvery high capacity for absorbing heat which causes rapid tion.

freezing of the melt and an especially uniform sized rup- EXAMPLE 1 ture of the cells.

It is pointed out that some materials may serve more 2 1nCh extruder as shown in FIGUR 1 is used, With than one function. For instance, some nucleating agents the lhlectlon Probe 6 Inches from the die Slit Which may also serve as fill or colorants, just as some prosmeasures 0.115 by 1 inch. The extruder screw is driven esshlg aids also double as blowing agents by a motor at screw speeds varying from 50 to 120 rpm,

The foams preferably have surface areas, as measured and a constant barrel Pltessure 0t ab0ut4500 P- A by the BmhauereEmmethTener nithotterhadpolyoxymethylene diacetate having a broad molecular sorption method, greater th ()4 {he/gm, but l than Weight distribution of 20,000-l00,000 made by blending 0 mtz/gm The density of the foams f bly i res ins of different molecular weights containing 1% by between 0.001 gm./cc. and 0.320 m./cc. Wall thickness welght of a tetpolyhler of 38% p y P 35% can be measured directly with a micrometer, or a single Polyhexamethylehe adtPamtde, and 27% *P Y wall can be analyzed for thickness by determining if Yt Sebaeamide e 01% by weight of 4,4"bhtY1tdehe X-rays or an electron beam will pass through it. Walls 0 blis(4'methyl'h'tertlaty'butyl P mixed with 2% over about 2 microns are opaque to X-rays and electron Flherglas havlng a diameter of 0-003 and a length of %4 beams. Wall thickness of from 2 microns to 100 microns and 1% haphthatehetis ted into the extruder' The are preferred The cells are preferably smaller than 1 output of the extruder varied from 50 to 80 lbs./hr., and across I 5 to 30 lbs./hr. of water was injected as the blowing These polyoxymethylenes have been found to make agent. The melt in the barrel was maintained-at the excellent cigatette filters, having the advantages of 1 following temperatures at the locations indicated in FIG- cost, ease of fabrication, low pressure drop, resiliency, URE 1 C, 2 3 1850 4 Cw a high surface area; they are odorless, tasteless, white, and T 6 The resulting e had a have high filter effieieheth By Way of comparison 50 to sity of 0.03 g./cc., and an average cell size of 0.5 mm., 80 mg. of polyoxymethylene foam removes as h which ranged from 0.1 to 1.0 mm. of WhlCh over 80% and nicotine as 90 to 140 mg. of cellulose acetate in the w Open cells and less than 20% were closed cells as Commercial cigarette filters tested udged by mlcroscopic examination of cell walls.

Cigarette filters can be made by passing the extruded Eafample 1 hepeated Sing the Same apparatus hut team in 1.ihheh form under a Wire brush running over a varying the conditions and the materials used. The remetal plate to shred the team into portions 1 to 3 inches sults are reported in Examples 2 to 4 set forth in-Table I. in length with a maximum diameter of about inch. a Example 3, a four'hole inch beading Che was The shreds are then assembled into a filter by the same stunted for the dyeused Eafamples 1, 2 and In technique by which tobacco is normally Wrapped with Example a dlameter radlal foamed film die was paper to form cigarettes. A preferred method of making usedh Polymer used In Example 2 was a eopolymer filters is to wrap the extruded foam ribbon with paper. 40 of approxlmately mole Percent CH2O units a In the drawing, FIGURE 1 is a cross section of an mole Percent CH2CH2O hits having an average extruder used for extruding toams molecular weight of about 35,000. The polymer used in FIGURE 2 is a side view of the foam shredder. Example 3 was a blend of 1/3 polyoxymethylehe diaee' FIGURE 3 is a View of the shreds being Wrapped tate havlng an average molecular weight of 60,000 and FIGURE 4 is a View of the completed hlteL /a polyoxymethylene diacetate having an average mo- The polyoxymethylene resin 1 is fed into the feed lecular Weight of 35,000. Example 4 used a blend of hopper a of extruder 3, maintained at from 150 to 200 polyexymethylene diacetflte having an average mo- C., and screw 4 rotated at a speed sufiicient to give a lecular welght of 60,000 and Of a polyoxymethylene pressure in excess of 200 psi at the die The blew diacetate having an average molecular weight of 35,000. the agent is injected undetptessure ltht-u probe 5 and 50 The polymer used in each of Examples 3 and 4 contained the resin extruded from die 6, whereupon the blowing 1% of a tehpolymer of 38% Polyeaprelaetflm, 35% P agent expands to form foam 7. The foam is cut into heXamethylene adipamide' and 27% polyheXamethylefle blocks and then fed on conveyor belt 8 under 'wire brush Sebacamide and 1% 0f y Y 9 to produce shredded foam 10 which is gathered in tertiary butyl P container 11. The foam is then poured into-a wrapper The properties of the foams made in Examples 2 to 4 12 as in FIGURE 3 which is then rolled up to form a are reported in Table II.

Table l CONDITIONS FOR FOAMING POLYOXYMETHYLENES Temperature, C. S Pressure, p.s.i. Rate, lbs./hr. Example Blowing Agent Additives Sghzh T1 T2 T3 T4 T5 T6 r. p .m B arrel Die Output Blowing Agent 2 210 200 170 165 165 9 vols. methyl/ 5% glass fiber.-. 30-45 1,500 50 25 3 ethyl ketone, 1 vol. chloroform. 3 215 195 185 185 185 Water 5% glass fiber 70 3,000 500 45 7 5% polysty- 4 215 195 185 185 140 Methyl/ethyl ZVZ ES hthalene 60-80 1,000 200 45 7 ljreztonelwater o g glass The foam produced in Example 1 is continuously passed under a rotating 3" diameter wire brush 3 inches wide made of 12 inch diameter steel wires, to cut the foam into shreds with a maximum diameter of about A; inch, averaging 1 inch in length, but varying from /2 to 3 /2 inches in length. The shreds are then rolled in cigarette papers to form a long filter which is then cut into 4 inch lengths and attached to various brands of filter cigarettes to replace the original filter and tested. The test results of this and various other polyoxymethylene foam filters are reported in Table III. The test used was the Cambridge Filter Disc Method in which a glass filter disc is inserted in the smoke train from an artificially smoked cigarette. The efiiciency of the cigarette filter is then ascertained by the weight of material caught by the glass filter disc. The pressure drop across the cigarette filter is ascertained before test smoking by a manometer filled with water with one end connected to the smoke train line and the other end open to the atmosphere so as to measure the pressure drop across the filter in inches of water. An air flow rate of 1050 cc./min. was used to measure pressure drop. A two second puff duration at 35 mL/puff is used in all the smoking tests. The filter disc was dried (1 hr. at 105 C.) before test smoking to avoid errors due to residual moisture on the glass filter. Runs 1 to 6 each used the tobacco end from the same brand of cigarette and smoked 49 mm. of cigarette. Runs 7 to 11 each used the tobacco end from the same brand of cigarette and smoked 46 mm. of cigarette. Run used a filter made by wrapping 3 ribbons of the foam extruded in Example 1 with paper and then cutting to 15 mm. lengths. Run 6 used a filter made by wrapping 4 ribbons of the foam of Example 1 with paper and then cutting to 15 mm. lengths. Runs 2 to 4 and 8 to 11 used the foam filters shredded by means of a wire brush as described above.

from which shreds are made can be wrapped in paper to make cigarette filters. Both the chopped foam and cylindrical methods produce effective filters although they are not as efiicient as the shredded filter or the foam ribbon type filters.

The foams of this invention have structures which are at least and preferably 75% ruptured celled. Other materials which are formed into open cell foams are formed first as closed cell foams and then crushed or otherwise mechanically treated to break the cell walls, rather than having the cell walls ruptured by the blowing agent upon extrusion. The procedure of this inven-v tion leaves residual cell walls which creates a large surface area while giving a good flow due to the large percentage of uniformly ruptured cells.

The extruded foams of this invention are useful as filter elements in a wide variety of applications. These applications include air conditioner filters, and solid-liquid,

separation filters such as automotive oil filter elements and dry cleaning solvent filters. The solid, as extruded foam can be used in these applications, and it has sufiicient strength and resiliency that little, if any, support is needed for such filter elements when used in low pressure applications.

We claim:

1.-A process of forming a predominantly ruptured polyoxymethylene foam for use as a cigarette filter comprising the steps of feeding a polyoxymethylene resin into an extruder maintained at from 150 C. to 250 C., and operated ata pressure above 200 pounds per square inch, and injecting a blowing agent into the polyoxymethylene resin melt before it leaves the die whereby the polyoxymethylene melt is blown to form a ruptured celled foam ribbon having a density of from 0.001 to 0.320 gram per cubic centimeter on leaving the extruder die, shredding the extruded foam to form shreds from /2 to 3 /2 inches in length with a maximum diameter of about /s inch, and wrapping said foam to form a cigarette filter.

2. The process of forming a cigarette filter comprising the steps of shredding a ribbon of ruptured celled polyoxymethylene' foam having a density of from 0.001 to 0.320 gram per cubic centimeter to form shreds from /2 to 3 /2 inches in length with a maximum diameter of /s inch, and wrapping said shreds to form a cigarette filter.

3. The process of forming a cigarette filter comprising the steps of wrapping a plurality of ruptured celled Table III PERFORMANCE OF POLYOXYMETHYLENE FOAMS IN CIGARETTE FILTE RS Pressure Material Wt. of Wt. Filter Drop in Passed per Run Filter Cigarette Materials Inches/Water Cigarette (mg) (mg) on Cigarette (mg) Plus Filter 1 Commercial Cellulose 838 130 2. 0 24 Acetate #1. 2 Foam of Example 1 845 69 1.1 19 3-- d0 750 80 1. 3 21 1. 7 24 0.8 19 68 0. 7 10 93 1. 4 25 Acetate #2. 8 Foam of Example 1 93 1. 5 22 9. do 56 3.0 19 10 do 59 4. 5 13 11 do 32 2. 1 24 length of the desired cigarette filter, or the foam ribbon foam polyoxymethylene ribbons having a density of from 0.001 to 0.320 gram per cubic centimeter and cutting the 70 wrapped ribbonsto the desired length.

'4. The process of claim 1 wherein the shredding step is carried out with a wire brush.

5. The process of claim 2 wherein the shredding step is carried out with a wire brush.

(References on following page) 7 8 References Cited by the Examiner 2,975,483 3/1961 Cooper et a1 264-143 3,006,346 10/1961 Golding 131--10 UNITED STATES PATENTS 3,039,908 6/1962 Parmele 156200 ggf ggg 2/1313 gavldsolz 2 3,067,147 12/1962 Rubens et a1 264-53 aney e a 5 2,653,987 9/1953 Batz 260-25 XR FOREIGN PATENTS 2,739,134 3/1956 Parry et a1. 264-205 1,227,864 3/1960 France. 2,770,241 11/1956 Winkler 131208 2,320 461 1 195g Muller 1 1 1 EARL M. BERGERT, Primary Examiner. 2,849,932 9/1953 Marogg 10 MELVIN D. REIN, J. J. BURNS, T. R. SAVOIE,

2,853,741 9/1958 Costa et al. 161402 XR Examiners. 

1. A PROCESS OF FORMING A PREDOMINANTLY RUPTURED POLYOXYMETHYLENE FOAM FOR USE AS A CIGARETTE FILTER COMPRISING THE STEPS OF FEEDING A POLYOXYMETHYLENE RESIN INTO AN EXTRUDER MAINTAINED AT FROM 150*C. TO 250*C., AND OPERATED AT A PRESSURE ABOVE 200 POUNDS PER SQUARE INCH, AND INJECTING A BLOWING AGENT INTO THE POLYOXYMETHYLENE RESIN MELT BEFORE IT LEAVES THE DIE WHEREBY THE POLYOXYMETHYLENE MELT IS BLOWN TO FORM A RUPTURED CELLED FOAM RIBBON HAVING A DENSITY OF FROM 0.001 TO 0.320 GRAM PER CUBIC CENTIMETER ON LEAVING THE EXTRUDER DIE, SHREDDING THE EXTRUDED FOAM TO FORM SHRED FROM 1/2 TO 3 1/2 INCHES IN LENGTH WITH A MAXIMUM DIAMTER OF ABOUT 1/8 INCH, AND WRAPPING SAID FOAM TO FORM A CIGARETTE FILTER. 